The present invention claims the benefit of Japanese Patent Application Nos. 2000-398871 filed on Dec. 27, 2000 in Japan, 2001-255780 filed on Aug. 27, 2001 in Japan, and 2001-352486 filed on Nov. 19, 2001 in Japan, which are all hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a wiring board and a method for fabricating a wiring board, and more particularly, to a multi-layer wiring board or a package for storing semiconductor elements and a method for fabricating a multi-layer wiring board or package.
2. Discussion of the Related Art
In recent years, various studies have been performed on multi chip modules (MCMs) in which a number of semiconductor elements are mounted on a build-up wiring board. Typically, by use of solder, electronic parts, such as chip capacitors, chip inductors, and chip resistors, for example, are mounted on the surface of a wiring layer formed on the surface of the wiring board.
Electronic parts that require predetermined regions for mounting are mounted on the surface of the build-up wiring board. Therefore, a limitation is imposed on miniaturization of the wiring board. Also, depending on the layout of wiring for surface mounting, parasitic inductance of the wiring, which is an undesirable property, becomes large. This factor hampers incorporation of such wiring boards into electronic devices of higher frequency.
In order to solve the aforementioned problems, various studies have been performed on methods for embedding electronic parts in an insulating substrate. Japanese Patent Application Laid-Open (kokai) No. 11-126978 discloses a method in which electronic parts are mounted by use of solder, in advance, on a wiring board having a transfer sheet formed from metallic foil, and then the parts are transferred. However, the method is problematic in terms of accuracy in positioning of the mounted parts.
Japanese Patent Application Laid-Open (kokai) No. 2000-124352 discloses a multi-layer wiring board in which an insulating layer is built up on electronic parts embedded on a core substrate. Where electronic parts are embedded in a substrate such as a core substrate, after a space between the substrate and the electronic parts is filled with an embedding resin, and an insulating layer and a wiring layer are built up on the substrate, the electrode of the electronic part must be electrically connected to the wiring formed on the insulating layer, through a metalization technique such as electroless plating.
The embedding resin is desirably colored black in order to prevent random reflection of light, which would otherwise raise problems when a wiring pattern is formed on the built-up insulating layer through exposure and development, or to reduce non-uniformity in color of the resin during curing of the resin. Therefore, carbon or a similar material must be incorporated, as a coloring agent, into the resin. However, when carbon, which is electrically conductive, is excessively incorporated into the embedding resin, the insulating property of the resin deteriorates. Therefore, it is important to design the method for coloring the resin black so that random reflection of light is prevented and non-uniformity in color of the resin is reduced during curing of the resin, with the insulating property between electronic parts or between wiring portions formed on the insulating layer being maintained.
A problem arises when a wiring board is used under high-frequency conditions in that there is loss of electrical signals in high-frequency regions. In order to reduce loss of electrical signals, an embedding resin used for embedding electronic parts in the wiring board must have low dielectric constant and exhibit low dielectric loss.
Accordingly, the present invention is directed to a wiring board and a method for fabricating a wiring board that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a wiring board having improved insulating properties, and for preventing random reflection of light, and reducing non-uniformity in color of the resin.
Another object of the present invention is to provide a method for fabricating a wiring board having improved insulating properties, and for preventing random reflection of light, and reducing non-uniformity in color of the resin.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the wiring board includes a substrate having an opening, and an electronic part placed in the opening, wherein a space left in the opening is filled with an embedding resin having a base color tone selected from black, blue, green, red, orange, yellow, and violet.
In another aspect, a method for fabricating a wiring board includes forming a first opening in a first substrate, placing a first electronic part in the first opening, and filling a space in the first opening with an embedding resin having a base color tone selected from at least one of black, blue, green, red, orange, yellow, and violet.
It is understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.